Bioerodible endoprostheses and methods of making the same

Abstract

Endoprostheses are disclosed.

What is claimed is: 
     
       1. An endoprosthesis comprising:
 a first portion having a first erodible metallic composition comprising magnesium or a magnesium alloy, the first portion having a first erosion rate, and a second portion having a second erodible metallic composition comprising an alloy of magnesium and an element selected from the group consisting of nitrogen, carbon, silicon, oxygen, sulfur, chromium, silver, gold, boron, and combinations thereof, the second portion having a second erosion rate slower than the first erosion rate, wherein the second portion is at least an outside surface of the endoprosthesis and the first portion is disposed inwardly of the second portion, the erosion rates being measured by suspending the endoprosthesis in a stream of Ringer's solution flowing at a rate of 0.2 m/second with all surfaces of the endoprosthesis being exposed to the stream of Ringer's solution, said Ringer's solution being a solution of distilled water containing 8.6 gram sodium chloride, 0.3 gram potassium chloride, and 0.33 gram calcium chloride per liter. 
 
     
     
       2. The endoprosthesis of  claim 1 , wherein the first erodible metallic composition is substantially pure magnesium. 
     
     
       3. The endoprosthesis of  claim 1 , wherein the first and second portions are circular in a transverse cross-section of the endoprosthesis. 
     
     
       4. The endoprosthesis of  claim 1 , wherein a thickness of the second portion is from about 10 nm to about 1000 nm. 
     
     
       5. The endoprosthesis of  claim 4 , wherein the thickness is from about 15 nm to about 100 nm. 
     
     
       6. The endoprosthesis of  claim 1 , wherein the erosion rate of the second portion is from about 0.01 percent of an initial mass of that portion per day to about 1 percent of the initial mass of that portion per day. 
     
     
       7. The endoprosthesis of  claim 6 , wherein the erosion rate is from about 0.1 percent of the initial mass of that portion per day to about 0.5 percent of the initial mass of that portion per day. 
     
     
       8. The endoprosthesis of  claim 1 , wherein the erosion rate of the second portion is from about 0.2 percent of an initial mass of that portion per day to about 10 percent of the initial mass of that portion per day. 
     
     
       9. The endoprosthesis of  claim 8 , wherein the erosion rate is from about 0.5 percent of the initial mass of that portion per day to about 5 percent of the initial mass of that portion per day. 
     
     
       10. The endoprosthesis of  claim 1 , wherein the erosion rate of the first portion is from about ten percent to about one-hundred percent greater than the erosion rate of the metallic portion having the lower erosion rate. 
     
     
       11. The endoprosthesis of  claim 1 , wherein the first and second portions are disposed within a longitudinal segment of the endoprosthesis. 
     
     
       12. The endoprosthesis of  claim 1 , wherein the endoprosthesis includes a plurality of segments, each segment including the first portion and the second portion, at least two of the segments having different erosion rates. 
     
     
       13. The endoprosthesis of  claim 12 , wherein at least two of the segments are arranged along a longitudinal length of the endoprosthesis. 
     
     
       14. The endoprosthesis of  claim 1 , wherein the endoprosthesis is adapted to erode sequentially along a longitudinal length of the endoprosthesis. 
     
     
       15. The endoprosthesis of  claim 1 , wherein the endoprosthesis is adapted to erode sequentially along a direction transverse to the longitudinal length of the endoprosthesis. 
     
     
       16. The endoprosthesis of  claim 1 , comprising an inner surface, an outer surface, and a portion between the inner and outer surfaces, wherein the portion between the inner and outer surfaces has an erosion rate higher than an erosion rate of the inner surface or the outer surface. 
     
     
       17. The endoprosthesis of  claim 1 , wherein the endoprosthesis is tubular in form. 
     
     
       18. The endoprosthesis of  claim 1 , wherein the endoprosthesis comprises a stent. 
     
     
       19. The endoprosthesis of  claim 1 , wherein the second portion completely surrounds the first portion. 
     
     
       20. A method of making a bioerodible endoprosthesis, the method comprising:
 implanting a material into a portion of a magnesium or magnesium alloy endoprosthesis, or precursor thereof, to create a bioerodible endoprosthesis comprising a first portion having a first metallic composition comprising the magnesium or the magnesium alloy and a second portion comprising an alloy of magnesium with the implanted material, wherein the implanted material comprises an element selected from the group consisting of nitrogen, carbon, silicon, oxygen, sulfur, chromium, silver, gold, boron, and combinations thereof, wherein the second portion is at least an outside surface of the endoprosthesis and the first portion is disposed inwardly of the second portion, wherein the second portion has a slower erosion rate than the first portion, the erosion rates being measured by suspending the endoprosthesis in a stream of Ringer's solution flowing at a rate of 0.2 m/second with all surfaces of the endoprosthesis being exposed to the stream of Ringer's solution, said Ringer's solution being a solution of distilled water containing 8.6 gram sodium chloride, 0.3 gram potassium chloride, and 0.33 gram calcium chloride per liter. 
 
     
     
       21. The method of  claim 20 , wherein the implanting employs a plasma. 
     
     
       22. The method of  claim 20 , further comprising, prior to implanting, applying a shielding to a portion of the endoprosthesis. 
     
     
       23. The method of  claim 22 , wherein the shielding comprises a coating. 
     
     
       24. The method of  claim 23 , wherein the coating comprises a polymer. 
     
     
       25. The method of  claim 22 , further comprising, after implanting, removing the applied shielding. 
     
     
       26. The method of  claim 20 , wherein the second portion completely surrounds the first portion.